This invention relates to a die for wirecoating a continuous strand. More particularly, the present invention relates to a die with portions that are movable with respect to each other to facilitate the threading of a strand in the die. The invention also relates to a method of manufacturing a wirecoated strand using the die. The invention is particularly useful in the production of wirecoated strands, which may be utilized in a subsequent process, such as the production of molded plastic articles.
A continuous strand can be covered with a sheath of material, which is referred to as wirecoating the strand. A strand can be wirecoated for several reasons, including to protect the strand from external elements, to strengthen the strand, and to provide a particular material on the strand for subsequent processing. A wirecoated strand may be chopped into pellets for use in a subsequent molding process.
Wirecoating involves the application of a sheath of resin on the outer surface of a strand as it passes through a die. Strands are typically wirecoated using a die which supplies the sheath of resin circumferentially about the strand. A continuous strand is attenuated through the die. The pressure coating of strands eliminates gaps or voids in the coating. When the strand breaks, the wirecoating process is interrupted and the strand must be rethread in the die.
Some conventional dies are unitary piece dies with a central aperture through which the strand is threaded. When the strand breaks, it is difficult to rethread the strand into the die and draw the strand out the outlet of the die to continue the operation.
Some coating assemblies include die halves that move relative to each other. Examples of such coating assemblies are disclosed in U.S. Pat. No. 4,419,958 to Roba and U.S. Pat. No. 4,688,515 to Rosebrooks.
Roba discloses a nozzle for the application of a protective resin to an optical fiber. The nozzle includes blocks A and B that are slidably interconnected by a set of four guide rods F1-F4 surrounded by respective coil springs 10 that are partly received in recesses 11 formed in the confronting block faces. A yoke 12 has a pair of legs C, D whose extremities are received in lateral notches of block A, to which they are secured by screws 14, and which engage in similar notches 15 of block B. A screw E is threaded into a neck 16 of yoke 12 and has a captive end retained in block B so that its rotation causes the blocks to approach each other against the resistance of springs 10. The nozzle body is produced by sliding the two aluminum blocks together. The arrangement relies on the operation of the springs 10 to separate the nozzle blocks.
Rosebrooks discloses a split coating head assembly for coating elongated strands. The head assembly includes mounting blocks 2, 32 that are movable together about an optical fiber. The mounting blocks 2, 32 are mounted opposite to each other on a platen 20. The platen 20 includes a screw 50 in a block 52 for retaining the mounting blocks 2, 32 in a tightly abutting relationship. The screw 50 is adapted to impinge upon the second mounting block 32, which is movable. When the mounting blocks are moved together, protrusions 24 on the first block enter bores 44 on the second block to accurately align the two half-die sets. The mounting blocks 2, 32 slide together around the fiber.
A need exists for an economical way to manufacture a wirecoated strand. Similarly, a need exists for a die in which a strand may be easily rethread to reduce the down time in the wirecoating process.
The shortcomings of the prior art are overcome by the disclosed dies which facilitate the threading of a strand in the dies. Each die embodiment includes portions that move relative to each other to allow access to the area between the portions.
One embodiment of a die embodying the principles of the invention includes an upper portion and a lower portion. Each die portion includes components corresponding to substantially half of a wirecoating die. Accordingly, when the die portions are adjacent each other, they form a complete wirecoating die. In the preferred embodiment, the upper portion is moveable relative to the lower portion, which is fixed.
Each portion is coupled to a support by a conduit through which resin can be supplied to the particular die portion. The upper portion is pivotally mounted to the support for movement between an upper position in which the die is open and a lower position in which the die is closed.
This die is used in an in-line wirecoating process in which a strand is wirecoated downstream from a bushing during a fiber forming process.
Another embodiment of a die embodying the principles of the invention is a sealable-slot die. This die embodiment includes a body and a nozzle disposed in the body. The nozzle and the die body have slots which are in fluidic communication with the exterior of the die. The slots are sized to permit a strand to be thread through them and into the interior of the nozzle.
A plate with an extension is placed on the die so that the extension seals the slots after a strand is thread in the die. This die is typically used in a low pressure system, such as a string binder wirecoating process.